They can call themselves anti-fascists but if they use threats and violence to prevent people they deem harmful from speaking then they are the real fascists.
i think you may be confusing fascism with violent direct action. violent direct action is a tactic used by fascists, but by no means does it only belong to fascists. afaik the mission statement of antifa is only about combating [certain] hate groups. however their goals actually play out is an entirely different story.